Radiotherapy consists of projecting onto a predetermined region of a patient's body, a radiation beam so as to destroy or eliminate tumours existing therein. Such treatment is usually carried out periodically and repeatedly. At each medical intervention, the radiation source must be positioned with respect to the patient in order to irradiate the selected region with the highest possible accuracy to avoid radiating adjacent tissue on which radiation beams would be harmful. If movement of a patient is detected during treatment, the treatment should be halted to avoid irradiating areas of a patient other than a tumour location.
For this reason a number of monitoring systems for assisting the positioning of patients during radiotherapy and detecting patient movement have therefore been proposed such as those described in Vision RT's earlier patents and patent applications U.S. Pat. Nos. 7,889,906, 7,348,974, 8,135,201, US2009/187112, WO2014/057280, and WO2015/008040.
In the systems described in Vision RT's patent applications, stereoscopic images of a patient are obtained and processed to generate data identifying 3D positions of a large number of points corresponding to points on the surface of an imaged patient. Such data can be compared with data generated on a previous occasion and used to position a patient in a consistent manner or provide a warning when a patient moves out of position. Typically such a comparison involves undertaking Procrustes analysis to determine a transformation which minimises the differences in position between points on the surface of a patient identified by data generated based on live images and points on the surface of a patient identified by data generated on a previous occasion.
Treatment plans for the application of radiotherapy are becoming increasingly complex with treatment apparatus having multiple or floating iso-centres. Also, there is an increasing trend to make use of higher doses of radiation during treatment in order to reduce overall treatment time. Such increasing complexity and higher dosages bring with them the increasing possibility of mistreatment. With the increasingly complex treatment plans, in addition to identifying the location and dosage of radiation at the surface of the patient, it would be desirable to identify the internal locations where radiation is applied and to obtain feedback on the radiation dosages applied internally during the course of treatment.
Another problem associated with monitoring patients during radiotherapy treatments is the fact that the appearance of the Cherenkov radiation emitted from a patient undergoing radiotherapy is dependent on the skin tone or colour, more specifically, on the level of chromophores present in the skin of the patient. The two chromophores which are of greatest significance are blood and melanin. This has the effect that any estimate of radiation received by the patient could be either too high or too low if the level of chromophores in the skin is not taken into account when determining that estimate. It will be understood that an incorrect estimation of the levels of radiation received by the patient estimate can have serious consequences to the well being of the patient as it is the estimates which are used to determine compliance with a radiation treatment plan which has been calculated to deliver the correct levels of radiation to the patient. Too low an estimate will result in increased levels of radiation being applied to comply with the treatment plan and lead to possible damage to the patient's tissue. Conversely, too low an estimate will result in not enough radiation being applied to the patient and lead to incomplete irradiation of the tumour being treated. This is particularly important as it has already been stated above that there is an increasing trend to make use of higher doses of radiation during treatment in order to reduce overall treatment time, with such higher dosages bringing with them the increasing possibility of mistreatment.